A multi-cylinder engine in an outboard engine system having a crankshaft disposed vertically is known from Japanese Patent Application Laid-open No. 5-60024, which comprises a plurality of intake pipes connected to a cylinder head respectively, a surge tank connected to upstream ends of the intake pipes, a throttle body connected to an upstream end of the surge tank, and a throttle guide connected to an upstream end of the throttle body.
The multi-cylinder engine described in Japanese Patent Application Laid-open No. 5-60024 suffers from a problem that the front end of the throttle guide largely protrudes forwards from an end of a crankcase, resulting in an increase in size of the entire engine, or only a small throttle guide can be mounted, because each of the intake pipes, the surge tank, the throttle body and the throttle guide are disposed substantially rectilinearly. Moreover, such known multi-cylinder engine also has a problem that a sufficient silencing effect cannot be expected, because it is difficult to ensure a space for disposition of an intake silencer of a large volume. Further, in the known multi-cylinder engine, three upper intake pipes other than a lowermost intake pipe are formed into an upward-convex arcuate shape and hence, an uppermost one of the intake pipes protrudes upwards from an upper surface of the cylinder block, thereby providing a possibility that such protrusion may influence the layout of the other components.
A multi-cylinder engine in an outboard engine system having a crankshaft disposed vertically is also known from Japanese Patent Application Laid-open No. 4-166496, in which a plurality of intake pipes connected to cylinders respectively and an intake chamber connected to upstream ends of the intake pipes are disposed along a side of a cylinder block.
In the multi-cylinder engine described in Japanese Patent Application Laid-open No. 4-166496, the intake pipes are disposed in parallel to one another at a given inclination angle and hence, it is easy to equally set the lengths of the intake pipes. However, there is a case wherein it is difficult to dispose the plurality of intake pipes in parallel to one another at the given inclination angle when taking account of the layout within an engine room and the plurality of intake pipes are forcibly disposed to extend radiately from a surge tank toward the cylinders which are disposed side by side in a vertical arrangement. If the intake pipes are disposed in this manner, the lengths of the intake pipes disposed horizontally to extend from the surge tank toward the cylinders are shortened, while the lengths of the intake pipes disposed inclined from the surge tank toward the cylinders are prolonged. Thus, the lengths of the intake pipes are non-uniform. If the lengths of the intake pipes are non-uniform in the multi-cylinder internal combustion engine in this manner, the following problem is encountered: it is difficult to effectively exhibit a pulsating effect of an intake system, thereby bringing about a hindrance to an increase in output from the engine.